1. Technical Field
The present invention relates to methods and apparatus for performing analyses on whole blood samples from microscopy images in general, and to automated version of the same in particular.
2. Background Information
Medical diagnostics often include analyses of a whole blood sample from a patient. One of the more popular diagnostics is a complete blood count (referred to as a “CBC”), which is a suite of tests that may include, in addition to the enumeration of the cellular components, red blood cell metrics, reticulocyte counts, and a leukocyte differential count (“LDC”; sometimes referred to as a “white blood cell differential”), which is the identification and enumeration of the types of white blood cells (WBCs) present in the blood sample.
Historically, the differential aspects of the CBC have been performed using separate methods from those used for enumeration. For example, the LDC portion of a CBC historically has been performed by smearing a small amount of undiluted blood on a slide, staining the dried, fixed smear, and examining the smear under a microscope. Reasonable results can be gained from such a smear, but the accuracy and reliability of the data depends largely on the technician's experience and technique. Blood smears are problematic for several reasons; e.g., the cells must be killed and fixed, which process precludes many types of supravital stains and analyses whose results depend upon living cells, and blood smears are labor intensive, cost prohibitive, and time consuming. For at least these reasons, blood smears are generally not favored for commercial applications.
Attempts to automate analyses of whole blood samples have met with some success, but typically have several drawbacks. For example, electrical impedance or optical flow cytometry instruments can be used to perform an LDC. Flow cytometry involves passing a diluted blood sample through a small vessel wherein electrical impedance or optical sensors can evaluate the constituent cells as they pass serially through the vessel. These instruments typically require fluid handling equipment and require the sample be diluted.
What is needed is an apparatus and method for performing automated analyses on a whole blood sample, including an LDC, which can overcome the limitations of the prior art, including the time required to perform the analysis, the operator skill level required to perform the analysis, and one that can provide greater versatility than known prior art methods and apparatus.